1. Field of the Invention
This invention relates to a feedback control system for pulse width modulation (PWM) controlling of the rotation, position, or the like of a motor or other controlled object or device.
2. Description of the Prior Art
Heretofore, digital servo circuits used for motor rotation control and the like, have made use of a PWM driving system which produced a PWM signal for driving a motor or other controlled object in response to control data produced according to control error data. In a digital servo circuit according to the prior art, duty data corresponding to control error data from a motor or other object to be controlled is supplied to a duty register which provides complement data to preset a counter each time the latter receives a load pulse, whereupon, the preset counter counts a master clock pulse, starting from the preset value, and provides a carry output from which the PWM control signal can be derived.
In the above described digital servo circuit according to the prior art, the frequency of the master clock pulse to be counted by the preset counter is dependent on the desired resolution of the PWM control signal and the carrier frequency thereof. Thus, the frequency of the master clock pulse can be reduced without reducing the resolution of the PWM control signal only by undesirably reducing the carrier frequency. On the other hand, if the carrier frequency is set at a desirable value, the master clock pulse frequency may become very high so that it becomes difficult to embody the digital servo circuit in an integrated circuit configuration.